Can you speak me about friction loss in pipes?
The Darcy-Weisbach equation with the Moody diagram are considered to be the most accurate model for estimating frictional head loss in steady pipe flow. Since the approach requires a not so efficient trial and error iteration an alternative empirical head loss calculation like the Hazen-Williams equation may be preferred:
f = 0.2083 (100/c)1.852 q1.852 / dh4.8655 (1)
where
f = friction head loss in feet of water per 100 feet of pipe (fth20/100 ft pipe)
c = Hazen-Williams roughness constant
q = volume flow (gal/min)
dh = inside hydraulic diameter (inches)
Note that the Hazen-Williams formula is empirical and lacks a theoretical basis. Be aware that the roughness constants are based on "normal" condition with approximately 1 m/s (3 ft/sec).
Online Hazens-Williams Calculator
The calculator below can used to calculate the head loss:
l - pipe or tube length (ft)
c - design coefficient determined for the type of pipe or tube
q - flow rate (gal/min)
dh - inside hydraulic diameter (inch)
Hazen-Williams equation in an Excel template
The Hazen-Williams equation is not the only empirical formula available. Manning's formula is common for gravity driven flows in open channels.
The flow velocity can be calculated as
v = 0.408709 q / dh2 (2)
where
v = flow velocity (ft/s)
The Hazen-Williams equation can be assumed to be relatively accurate for piping systems with Reynolds Numbers above 105 (turbulent flow).
1 ft (foot) = 0.3048 m
1 in (inch) = 25.4 mm
1 gal (US)/min =6.30888x10-5 m3/s = 0.227 m3/h = 0.0631 dm3(liter)/s = 2.228x10-3 ft3/s = 0.1337 ft3/min = 0.8327 Imperial gal (UK)/min
Note! The Hazen-Williams formula gives accurate head loss due to friction for fluids with kinematic viscosity of approximately 1.1 cSt. More about fluids and kinematic viscosity.
The results for the formula is acceptable for cold water at 60 oF (15.6 oC) with kinematic viscosity 1.13 cSt. For hot water with a lower kinematic viscosity (0.55 cSt at 130 oF (54.4 oC)) the error will be significant.
Since the Hazen Williams method is only valid for water flowing at ordinary temperatures between 40 to 75 oF, the Darcy Weisbach method should be used for other liquids or gases.
HOPE THIS DIDN'T GET YOU TOO AROUSED. :rofl:
